[albertino]

Originally Posted by justinwschang

The SIMPLE PAST expresses action that happened at a time that has gone by and finished, such as yesterday, just now, before this, two months ago:She was in a white skirt yesterday (not: She has been in a white skirt yesterday).

The PRESENT PERFECT expresses: (a) Action completed as of now (vs. simple past, which expresses action that occurred in the past); or (b) Action continuing (from the past) up to now.

Completed as of now: (i) He has eaten his lunch; (ii) Have they been to Toronto? (= so far/up till now, have they been to.....).

Continuing up to now: (i) We have been here since yesterday (= still here); (ii) She has lived alone for five years (= still alone); (iii) They have been teachers for a year (= still teachers); (iv) I have lost my pen (= still not found) vs. I lost my pen (= lost, some time in the past, perhaps now found?).

The simple past is NOT used for unfinished time, for which we use the present perfect: We have been here since yesterday (not: We were here since yesterday).

The present perfect is NOT used for finished time, for which we use the simple past: He arrived yesterday (not: he has arrived yesterday).

DIFFERENCE BETWEEN THE TWO TENSES: The simple past expresses just the occurrence of an action in the past; the present perfect expresses the completion, or continuation, of that action as of the present moment.

He has eaten lunch (= completed as of now, eaten as of now); He ate lunch (= occurred then, ate then); I have waited since noon (= continuing up to now, still waiting); I waited at noon (= occurred then, waiting then); He has been there all day (= continuing up to now, still there); He was there all day (occurred then, was being there then).

Yes, Justinwschang, you're right. I have made a mistake in using the past tense rather than the past perfect in "When you were living in London, have you ever tried jellied eels?" Thanks for pointing it out.